1. Field of the Invention
The present invention relates to a liquid crystal display device and a method of fabricating a liquid crystal display device, and more particularly, to an in-plane switching mode liquid crystal display device and a method of fabricating an in-plane switching mode liquid crystal display device.
2. Description of the Related Art
In general, a liquid crystal display (LCD) device is capable of adjusting light transmission ratios of liquid crystal cells to display image data by individually supplying data signals corresponding to the image data to the liquid crystal cells. Accordingly, the LCD device includes a liquid crystal display panel in which liquid crystal cells are aligned in a matrix configuration and a driver integrated circuit (IC).
The liquid crystal display panel includes a color filter substrate and a thin film transistor (TFT) array substrate that oppose each other and a liquid crystal layer between the color filter substrate and the TFT array substrate. The TFT array substrate includes data lines for transmitting data signals supplied from a data driver IC to the liquid crystal cells and orthogonal gate lines for transmitting scan signals supplied from a gate driver IC, wherein the liquid crystal cells are defined at intersections of the data lines and gate lines. The gate driver IC sequentially supplies scan signals to the gate lines to sequentially select liquid crystal cells on a one by one basis. In addition, the data driver IC supplies data signals to the liquid crystal cells of selected gate lines.
Although twisted nematic mode LCD devices are commonly used as high definition display devices having low power consumption, they have a narrow viewing angle. This is due to refractive anisotropy of liquid crystal molecules, wherein the liquid crystal molecules aligned in parallel to the substrate are aligned almost vertically to the substrate when a voltage is supplied to the LCD panel. Accordingly, in-plane switching mode LCD devices have been developed to overcome this disadvantage.
Generally, the in-plane switching mode LCD devices include an upper substrate having color filters, a lower substrate having TFTs, a common electrode, pixel electrodes, and a liquid crystal layer formed between the upper and lower substrates.
FIG. 1 is a plan view of an in-plane switching mode liquid crystal display (LCD) device according to the related art. In FIG. 1, a pixel region is defined by arranging a plurality of gate lines 1 along a first direction and a plurality of data lines 2 along a second direction perpendicular to the first direction. In general, an N×M matrix of pixels are formed such that an N-number of gate lines 1 and an M-number of data lines 2 are provided on a substrate. A TFT composed of a gate electrode 5, a semiconductor layer 15, and source/drain electrodes 6a and 6b is disposed at each intersection between the gate and data lines 1 and 2, and a common line 3 is arranged in the pixel region approximately parallel to the gate line 1. In addition, pixel and common electrodes 8 and 9 are arranged in parallel to each other for switching the liquid crystal molecules of the LCD device. The pixel electrode 8 is connected to the drain electrode 6b of the TFT and the common electrode 9 is connected to the common line 3. Accordingly, a voltage is supplied through the TFT and a lateral electric field is generated between the pixel electrode 8 and the common electrode 9.
FIG. 2 is a cross sectional view along I–I′ of FIG. 1 according to the related art. In FIG. 2, the LCD device includes a TFT substrate 10 having the TFT formed on a transparent substrate 7, the common electrode 9, and the pixel electrode 8, and a color filter substrate 20 having a light-shielding layer (i.e., black matrix) 21, a color filter 23, and a overcoat layer 25. In addition, a liquid crystal layer 30 is formed between the TFT substrate 10 and the color filter substrate 20, and a spacer 31 is positioned in the liquid crystal layer 30 to maintain a uniform cell gap between the TFT and color filter substrates 10 and 20.
The TFT includes a gate electrode 5, source/drain electrodes 6a and 6b, a semiconductor layer 15, and an ohmic contact layer 14. In addition, a gate insulating layer 11 is formed between the gate electrode 5 and the semiconductor layer 15.
Within the pixel region, the common electrode 9, which is formed together with the gate electrode 5 of the TFT, and a pixel electrode 8, which is formed together with the source/drain electrodes 6a and 6b, are formed at a predetermined interval, and a passivation layer 13 is formed over an entire surface of the TFT and an upper portion of the pixel region. However, since the pixel electrode 8 and the common electrode 9 are formed on the same substrate, an aperture ratio of the LCD device is degraded. For example, since the pixel electrode 8 and the common electrode 9 are made of opaque metal materials, light is not transmitted from a backlight device within a region where the pixel and common electrodes 8 and 9 are formed. Accordingly, an area of the opening portion is reduced by an area corresponding to the the pixel and common electrodes 8 and 9. In order to solve the problem, the aperture ratio is improved by forming the common electrode 9 and the pixel electrode 8 of transparent materials.
FIG. 3 is a plan view of another in-plane switching mode liquid crystal display device according to the related art, and FIG. 4 is a cross sectional view along II–II′ of FIG. 3 according to the related art. In FIGS. 3 and 4, an aperture ratio can be improved by forming pixel and common electrodes 18 and 19 positioned within a pixel region of transparent materials. In addition, a passivation layer 13 may be formed of organic materials having low dielectric constants between the data line 2 and the common electrode 19. Accordingly, the common electrode 19 is formed along a boundary of two adjacent pixel electrodes 18, such as an upper portion of the data line 2, and generates a lateral electric field (solid line) between the two adjacent pixel electrodes 18.
However, as shown in FIG. 4, the data line 2 positioned in a lower portion of the common electrode 19 generates another electric field (dotted line) with the pixel electrode 18 that is adjacent to the common electrode 19. Accordingly, the data line distorts the lateral electric field between the common electrode 19 and the pixel electrode 18. Thus, light leaks along a marginal region of the pixel electrode 18 between the data line 2 and the adjacent pixel electrode 18, thereby generating cross-talk on a display screen.